1. Field of the Invention
The present invention relates to an anti-reflection film, and a silica layer which can be suitably used for this.
2. Related Art
Transparent substrates such as glasses and plastics are used in various displays used in liquid crystal displays, plasma displays, CRT displays of computers, word processors, televisions, display plates and the like, indicators such as instruments and the like, rearview mirrors, goggles, window glasses and the like. Since letters and figures and other information are read out through those transparent substrates, there is a drawback that, when the light is reflected on the surfaces of the transparent substrates, it becomes difficult to read out the information.
Currently, in order to solve the above drawbacks, light reflection is prevented by using an anti-reflection film comprising a substrate, a hard coated layer, and a layer stack formed by depositing a plurality of thin layers having different refractive indices (e.g. low refractive index layer, intermediate refractive index layer, high refractive index layer), and applying the anti-reflection film on the surface of the above transparent substrate.
In this case, it is known that provision of a layer having a small refractive index for effectively preventing light reflection, so-called a low refractive index layer on an outermost layer in the anti-reflective film with a layer stack provided thereon (surface opposite to a substrate of the anti-reflection film) is preferable and, as the layer having a small refractive index, a silica layer is suitably used.
In addition, as a method of forming a layer stack, a method of formation by a sputtering method or a evaporation method has been previously known.
However, when a layer stack is formed by a sputtering method, there is a problem that precision in layer formation is better, but since a formation rate is very small, the productivity is deteriorated. In addition, when a layer stack is formed by a evaporation method, there is no problem in a rate of layer formation, but formation precision is bad and, therefore, yield is deteriorated, and this may lead to the high cost of the anti-reflection film, being problematic.
In order to solve the aforementioned problems, currently, a method of forming a layer stack by a plasma CVD method is developed. By forming a layer stack by a plasma CVD method, a formation rate can be dramatically heightened as compared with formation by a sputtering method or the like.
However, when a layer stack is formed by a plasma CVD method, the following problems arise newly.
The first problem is that the adherability between respective thin layers forming a layer stack is deteriorated as compared with the case where a layer stack is formed by a sputtering method or a evaporation method.
In addition, the second problem is that, when a titanium oxide layer functioning as a high refractive index layer among thin layers forming a layer stack is formed by a plasma CVD method, the titanium oxide layer is bad in the resistance to wet heat, and a refractive index is not stable in some cases.
A main object of the present invention is to provide, in an anti-reflection film having a layer stack, an anti-reflection film in which each thin layer constituting a layer stack has the better resistance to wet heat and, therefore, the optical properties are excellent due to stable refractive index in each thin layer and, further, a formation rate is high, and the adherability of each thin layer is also excellent.
In addition, apart from the above problems, there is a new problem that a layer stack of an anti-reflection film prepared by a plasma CVD method is inferior in the resistance to chemicals. For example, in a process of preparing an anti-reflection film, there is a process of treating a layer stack with an alkali in some cases and, upon this, a thin layer formed by a plasma CVD method is dissolved in an alkali solution in some cases.
In particular, a low refractive index layer in a layer stack in an anti-reflection film is used as an outermost layer of a layer stack in many cases and, therefore, since the layer is directly contacted with an alkali solution upon the alkali-treatment, the layer is dissolved in many cases.
In order to solve such the problem, a protecting film is adhered on an outermost layer of a layer stack upon the alkali-treatment, but this can not be said to be a fundamental resolution strategy. In addition, since it is necessary to detach the protecting film, there is a problem that a preparation process becomes complicated.
The present invention has been achieved in order to solve the above problems. It is an object of this invention to provide an anti-reflection film which is excellent in the resistance to chemicals even when formed by a plasma CVD method, and a silica layer.
The present invention for attaining the aforementioned object, firstly, an anti-reflection film having a substrate, a hard coated layer situated on the substrate, and a layer stack which is situated on the hard coated layer and in which a plurality of thin films are deposited, wherein the layer stack is formed by depositing a thin layer formed by a plasma CVD method, and a thin layer formed by a sputtering method or a evaporation method.
According to this invention, since a layer stack constituting an anti-reflection film is formed by depositing a thin layer formed by a plasma CVD method and a thin layer formed by a sputtering method or a evaporation method, the productivity can be improved as compared with formation of all thin layers constituting a layer stack by a sputtering method or a evaporation method and, on the other hand, the resistance to wet heat of each thin layer can be improved and, at the same time, the adherability between respective layers can be improved.
In addition, in the first invention, it is preferable that, among the aforementioned thin layers forming a layer stack, a thin layer formed by a plasma CVD method is a low refractive index layer having a refractive index of not less than 1.40 and not greater than 1.46 (xcex=550 nm), or an intermediate refractive index layer having a refractive index of not less than 1.55 and less than 1.80 (xcex=550 nm), and a thin layer formed by a sputtering method or a deposition layer is a high refractive index layer having a refractive index of not less than 1.80 (xcex=550 nm).
According to this aspect, a formation rate can be heightened by forming a low refractive index layer or an intermediate refractive index layer which dose not give rise to a problem when formed by a plasma CVD method (that is, dose not give rise to a problem in the resistance to wet heat) by a plasma CVD method and, on the other hand, a refractive index of a high refractive index layer can be stabilized by forming only a high refractive index layer in which a refractive index is not stabilized in some cases due to bad resistance to wet heat when formed by a plasma method, by a sputtering method.
In addition, in the first invention, the layer construction of the layer stack may be an intermediate refractive index layer, a high refractive index layer and a low refractive index layer from a hard coated layer side.
Further, in the first invention, the layer construction of the layer stack may be a high refractive index layer, a low refractive index layer, a high refractive index layer and a low refractive index layer from a hard coated layer side.
In addition, in the first invention, a low refractive index layer or an intermediate refractive index layer formed by the plasma CVD method may be a silicon layer, and a high refractive index layer formed by a sputtering method or a evaporation method may be a titanium oxide layer or an ITO layer exhibiting a high resistance.
The present invention for attaining the aforementioned object is, secondly, an anti-reflection film having a substrate, a hard coated layer situated on the substrate, and a layer stack which is situated on the hard coated layer and in which a plurality of thin layers are deposited, wherein a silica layer formed by a plasma CVD method, having a refractive index of 1.40-1.46 (xcex=550 nm), and having infra-red absorption based on Cxe2x80x94H stretching vibration at 2800-3000 cmxe2x88x921 of not greater than 0.1 cmxe2x88x921 and infra-red absorption based on Sixe2x80x94CH3 stretching vibration at 1200-1400 cmxe2x88x921 of not greater than 0.1 cmxe2x88x921, as a low refractive layer is present in the aforementioned layer stack.
According to this invention, since a silica layer as a low refractive index layer in an anti-reflection film is formed by a plasma CVD method and has a refractive index of 1.40-1.46 (xcex=550 nm), the silica layer is excellent in the adherability, and has a high formation rate. In addition, the silica layer is excellent in the optical properties and can effectively prevent light reflection and, at the same time, can be used as a low refractive index layer in a layer stack in an anti-reflection film and, as a result, the better anti-reflection film is obtained. Further, since infra-red absorption based on Cxe2x80x94H stretching vibration at 2800-3000 cmxe2x88x921 and infra-red absorption based on Sixe2x80x94CH3 stretching vibration at 1200 to 1400 cmxe2x88x921 are 0.1 cmxe2x88x921 or smaller, respectively, that is, are below a detection limit, it is clear that little organic components are contained in a silica layer and, as a result, a silica layer is thought to be excellent in the resistance to chemicals, although formed by a plasma CVD method.
In addition, in the second invention, it is preferable that a raw material upon formation of a silica layer as the low refractive index layer by a plasma CVD method is Si alkoxide.
In addition, in the second invention, it is preferable that the aforementioned Si alkoxide as a raw material is tetramethoxysilane.
Further, in the second invention, at least one of an intermediate refractive index layer having a refractive index of not less than 1.55 and less than 1.80 (xcex=550 nm) or a high refractive index layer having a refractive index layer not less than 1.80 (xcex=550 nm) may be in the aforementioned layer stack, in addition to a silica layer as a low refractive index layer.
In addition, in the second invention, the layer construction of the aforementioned layer stack may be an intermediate refractive index layer, a high refractive index layer, and a silica layer as a low refractive index layer from a hard coated layer side.
Still further, in the second invention, the layer construction of the aforementioned layer stack may be a high refractive index layer, a silica layer as a low refractive index layer, a high refractive index layer, and a low refractive index layer from a hard coated layer side.
The present invention for attaining the aforementioned object is, thirdly, an anti-reflective film having a substrate, a hard coated layer situated on the substrate, and a layer stack which is situated on the hard coated layer and in which a plurality fo thin layers are deposited, wherein a silica layer, as a low refractive index layer, formed by a plasma CVD method, having a refractive index of 1.40-1.46 (xcex=550 nm) and having infra-red absorption based on Cxe2x80x94H stretching vibration at 2800-3000 cmxe2x88x921 of not greater than 0.1 cmxe2x88x921 and infra-red absorption based on Sixe2x80x94CH3 stretching vibration at 1200-1400 cmxe2x88x921 of not greater than 0.1 cmxe2x88x921, and a high refractive index layer formed by a sputtering method or a evaporation method and having a refractive index of not less than and less than 1.80 (xcex=550 nm) are present in the layer stack.
In the third invention, an intermediate refractive index layer having a refractive index of not less than 1.55 and less than 1.80 (xcex=550 nm) may be present in the layer stack.
In addition, in the third invention, the layer construction of the layer stack may be an intermediate refractive index layer, a high refractive index layer, and a silica layer as a silica layer as a low refractive index layer from a hard coated layer side.
Further, in the third invention, the layer construction of the layer stack may be a high refractive index layer, a silica layer as a low refractive index layer, a high refractive index layer, and a silica layer as a low refractive index layer from a hard coated layer side.
The present invention for attaining the aforementioned object is, fourthly, a silica layer as a low refractive index layer in an anti-reflection film such that it is formed by a plasma CVD method, a refractive index thereof is 1.40-1.46 (xcex=550 nm), and infra-red absorption based on Cxe2x80x94H stretching vibration at 2800-3000 cmxe2x88x921 and infra-red absorption based on Sixe2x80x94CH3 stretching vibration at 1200-1400 cmxe2x88x921 are 0.1 cmxe2x88x921 or smaller, respectively.
According to this invention, since a silica layer is formed by a plasma CVD method, and has a refractive index of 1.40-1.46 (xcex=550 nm), the silica layer is excellent in the optical properties, can effectively prevent light reflection and, at the same time, and can be used as a low refractive index layer in a layer stack of an anti-reflection layer. Further, since infra-red absorption based on Cxe2x80x94H stretching vibration at 2800-3000 cmxe2x88x921 and infra-red absorption based on Sixe2x80x94CH3 stretching vibration at 1200-1400 cmxe2x88x921 are 0.1 cmxe2x88x921 or smaller, respectively, that is, are below a detection limit, it is clear that little organic components are contained in a silica layer and, as a result, a silica layer is thought to be excellent in the resistance to chemicals although formed by a plasma CVD method.
The present invention further includes other many embodiments illustrated in detail below. In addition, a person skilled in the art can understand that the present invention includes other many embodiments which are altered or modified from the present invention based on the detailed description below without departing the concept and category of the present invention which is limited only by the description of claims.